354 THE ALCALIGENES— DYSENTERY— TYPHOID GROUP 
and colorless; frequently they attain a diameter of from 1 to 3 mm. 
The colonies are indistinguishable from those produced by bacilli of 
the typhoid and paratyphoid groups. There is moderate growth 
along the line of inoculation in gelatin, but no liquefaction. In broth 
after eighteen to twenty-four hours' growth a uniform turbidity 
develops, somewhat more luxuriant in glucose than in plain broth. 
After several days' growth in plain broth a delicate pellicle frequently 
appears on the surface of the latter medium. In milk moderate 
development takes place with no coagulation. There is an initial 
acidity followed after from two to five days by an alkaline reaction, 
which increases somewhat in intensity with the age of the culture. 
On potato the growth is very similar to that of the typhoid bacillus; 
on acid potato the growth is almost invisible; on alkaline potato the 
growth is brownish and of moderate luxuriance. 
Fig. 49. — Bacillus dysenterise. Shiga type, bouillon culture. X 1000. 
The dysentery bacilli are aerobic, facultatively anaerobic bacilli 
whose limits are approximately the following: minimum temperature 
of gro^^i:h 8° C; maximum 42° to 44° C; optimum 37° C. 
Cultures of dysentery bacilli vary somewhat in their resistance to 
heat. The majority of cultures are killed by an exposure of ten min- 
utes at 65° C. Some strains, however, are only killed by an exposure 
of ten minutes at 70° C. The organisms are moderately resistant to 
cold. Cultures may retain their viability in the ice-box, 6° to 10° C, 
for nearly two months. In sterile water the organisms at ordinary 
temperatures do not, as a rule, survive more than a week. PfuhP 
has found that dysentery bacilli may remain alive for one hundred and 
one days in moist soil protected from sunlight; in dry soil under 
otherwise the same conditions they do not survive more than thirty 
days. In cheese and in butter they remain alive for at least nine 
days, and in sterile milk for about three weeks. Dried on linen, 
they also survive about three weeks. 
1 Ztschr. f. Hyg., 1902, 40, 555. 
